The present invention relates to restrained pipe joints and, more specifically, to a pipe joint including a snap ring which prevents axial movement of the bell end of one pipe relative to the spigot end of an attached pipe.
The use of pipe joints, couplings and fittings of the socket and spigot type is well known and is shown, in U.S. Pat. No. 2,991,092, issued to Jack W. MacKay on July 4, 1961. The MacKay patent, which is assigned to the assignee of the present invention and hereby incorporated by reference, discloses the use of a double sealing gasket for socket and spigot type joints. The simplicity and tightness of the seal in the joint disclosed in the MacKay patent makes this joint useful for a wide variety of applications.
Such joints are continually subject in use to axial forces which tend to move one pipe away from the adjacent and connecting pipe. Numerous attempts have been made to construct pipe joints designed to withstand axial forces. Such pipe joints are often complex in construction and may require extensive modification of the basic socket and spigot ends of the connecting pipes. Often these pipe joints require some form of bolt arrangement designed to clamp one pipe to the adjacent pipe. Such bolt type of pipe joints are generally ill suited for allowing angular deflection between the spigot end of one pipe and the attached socket or bell end of another pipe. It should be noted that it is generally desirable for a pipe joint to accommodate limited angular deflection or pivoting movement between the spigot end of the pipe and the attached socket end of the pipe making up a particular pipe joint.
Another form of restrained pipe joint provides the spigot end of the pipe with a locking collar welded or otherwise attached to it. In such an arrangement, the bell member of the socket pipe is inserted between the locking collar and the spigot end of the pipe itself, whereupon the locking collar is rotated to an angular position relative to the bell member and locked therein such that the bell member may not be axially displaced relative to the locking collar and spigot. Although it is generally advantageous to lessen stresses by allowing some rotation between socket and spigot, this rotation feature may be disadvantageous in certain respects. For example, the tolerance of the socket or bell member must be tightly controlled. If the bell member is too large it may prevent rotation and locking or it may bind on the locking collar of the spigot section making rotation of the locking collar extremely difficult. Alternatively, if the bell member is too small, it will not prevent back rotation of the locking collar, raising the possibility that the repeated application of fluid through the pipe may cause the locked joint to be undone. Thus, this structure must contain some means to prevent unintentional rotation of the locking collar. This structure is usually complex and is less than desirable in strength and cost.
Another form of known restrained pipe joint employs a snap-ring to secure the spigot and socket against separation. Snap-rings have generally required substantial modification to the basic spigot and socket interface, and usually need a slot or window in the socket pipe for allowing adjustment to the snap-ring diameter to lock or unlock the joint. This slot or window is a point of weakening stress concentration and presents a problem in construction. Accessability to the snap-ring also becomes a serious problem. In addition, if the gasket is carried by the spigot member and the snap-ring is carried by the bell member, as is the case in the prior art, the gasket must pass by the snap-ring member during installation. The gasket is thus vulnerable to damage in installation.
An invention which avoids or minimizes most of these problems is described in detail in U.S. patent application Ser. No. 242,925, now U.S. Pat. No. 4,428,604, issued Jan. 31, 1984 in the name of Randall C. Conner and titled "Restrained Pipe Joint and Associated Snap-Ring". This patent, assigned to the assignee of the present invention and hereby incorporated by reference, discloses a pipe joint having a snap ring having continuous annular external and internal contours (i.e., no slots or windows). A continuation-in-part (CIP) application, Ser. No. 390,881 to this patent was filed June 21, 1982. The CIP application issued June 26, 1984 as U.S. Pat. No. 4,456,288. Both the '604 patent and its CIP disclose ring adjustors used to press a snap ring inward against a spigot end of a pipe or alternately press the snap ring outward against a socket end of a pipe. The CIP application discloses a design which allows easier rotation between attached pipes than the basic design in U.S. Pat. No. 4,428,604. A divisional application of Ser. No. 242,925, was filed on Nov. 1, 1983 and assigned Ser. No. 547,680 and issued as U.S. Pat. No. 4,524,505 on June 25, 1985. The CIP and divisional applications are assigned to the assignee of the present invention and are hereby incorporated by reference.
As mentioned above, it is sometimes advantageous to provide restrained pipe joints that are capable of significant amounts of angular deflection. Specifically, a pipe joint wherein a pipe can have its axis deflected out of line with the axis of the attached pipe is useful in adjusting the pipe joint for unstable soils and other problems in the layout and installation of the pipes.
The amount of deflection for the pipe joint of the type described in U.S. Pat. No. 4,428,604 is a function of the assembly clearance. However, the assembly clearance is purposely limited by design to minimize the possibility of failure (i.e., joint application) caused by stress concentrations. If the angle of deflection is too great, stress would be concentrated on a relatively small bearing area. A joint separating thrust could then cause joint separation.
Although pipe joints designed with a ball-and-socket arrangement can accommodate great angles of deflection, the cost of such pipe joints is quite high. Such pipe joints have a spherical ball at the end of one pipe to fit within a spherical socket at the end of an attached pipe and are generally not cost effective except for quite severe pipe joint applications.
Pipe joint designs often require one to field-cut pipes in restrained joint locations in order to position fittings and/or valves or other fixtures at their desired positions in the pipeline, in lieu of adequate shop drawings or layouts of prefabricated systems. This presents a significant design problem when the thrust resisting capabilities of a restrained joint are heavily dependent on the quality of the fabrication work preformed to produce it. In the case of restrained joints for ductile iron pipes, this required shop fabrication procedure often requires welding of a raised member(s) on the spigot and/or bell. The welding of ductile iron pipes requires equipment and skills sometimes not easily obtainable in the field by those who install the pipes. Consequently, it is desirable in many cases to offer alternate means of assembling restraining members onto the pipes in the field which may be accomplished without the use of elaborate equipment and skilled labor.
One such restraining means that may be used to produce field-adaptable restrained joints is the mechanical joint retainer gland, employing set-screws to lock and hold a gland to the spigot of a pipe. Such structures use multiple radial set-screws set through tapped holes in the lip of the gland, and the cupped points on the set-screws are used to set into the surface of the spigot pipe to prevent endwise separation of the pipes. With such a restraining mechanism, it is possible to field cut a pipe for length adjustment, assemble the rubber-gasketed joint, and then tighten the set-screws to produce a reliable field-cut restrained joint. This may be accomplished with relatively unskilled labor.
However, such retainer gland pipe joints are very limited in thrust capabilities and pipe size. The thrust resisting capabilities of the retainer gland joint are directly dependent on the holding power of the set-screws. This holding power is determined primarily by the initial torque of (and indentation of the spigot pipe by) the set-screws. When subjected to joint separating force, the set-screws subject the indented pipe metal to shearing forces in the direction of thrust. Thus, the thrust resisting capabilities of the joint are primarily a function of this shearing resistance plus frictional resistance, which is a function of normal (or radial) force between the pipe metal and screw. Due to the greater thrusts caused by unbalanced internal pressure or other forces and the increasing flexibility of the pipe walls, ordinary mechanical joint set-screw glands become less desirable with increasing pipe size. It is not practical to increase the size, torque, or number of set-screws enough to achieve adequate thrust resisting capabilities in larger pipe. An increase in size or torque on the set-screws results in increased localized deflection or failure in the spigot pipe wall with the possibilities of leakage by the gasket due to lack of adequate gasket compression in service and/or structural failure of the pipe wall. Thus, an increase in number and/or size of set-screws results in increased cost, more difficulty in installation, and increases in stress in the gland and spigot.
Another problem with numerous prior art pipe joints is that minor variations in size due to manufacturing tolerances pose a design trade-off between making a joint especially secure but difficult to assemble or making the joint easy to assemble but less secure than otherwise desirable.
Prior art pipe joints have generally been disadvantageous in that they may appear to be secured or locked while the joint is actually improperly installed causing leaks and even total failure of the pipe joint.
Accordingly, whereas numerous techniques have been developed for axially restraining pipe joints from separation due to axial forces, the techniques are subject to several disadvantages and it is therefore a principal object of the present invention to provide an improved pipe joint locked against separation, while allowing for significant angular displacement between adjacent pipes without concentrating great stress on a limited bearing area.
A still further object of the present invention is to provide an improved pipe joint wherein rotation of the socket or bell end pipe relative to the spigot end pipe will not cause unlocking of the joint.
Yet another object of the present invention is to provide an improved axially restrained pipe joint wherein assembly may be accomplished conveniently and without a need for skilled labor.
A further object of the present invention is to provide a method and pipe joint adapted for easily determining if the pipe joint is properly locked.
Another object of the present invention is to provide a pipe joint of improved deflection performance and retention strength in the deflected position.
A still further object of the present invention is to provide a pipe joint which facilitates dependable field adaptability.
Still another object of the present invention is to provide for a restrained pipe joint including a socket member with only continuous internal or external annular contours. This pipe joint may include a socket member with no holes, slots, windows, or other discontinuities. In addition, no internal or external locking lugs may be required in the locking collar or socket member.
Yet another object of the present invention is to provide a snap ring and associated method of making a snap ring which minimizes the impact of minor variations in manufacturing tolerances.